imaginary and real world signals

my professor signals and system talk"we have two signals real signal and imaginary signals.WE CAN PLAY WITH IMAGINARY SIGNALS but cannot with real signals and we can always transform imaginary signals into real signals"

could anyone understand what he trying to say.Why does he say we can play with imaginary signals

I would need a better idea of the context within which the statement is made, but my guess is that all he is saying is that we can transform a real world signal representation into a representation that involves complex numbers and then work (i.e., "play") with that representation and then, at the end of the day, transform the final result back into a real world signal representation.

This is exactly what we do when we convert an sinusoidal signals into "phasors", transform inductances and capacitances into "impedances", or take the Laplace or Fourier transform of signals.

i am sailing in boat moving 3 units in north moving 4 units in east having 3+4j as vector now i want to rotate it to 90 degree counter clockwise so i just multiply by i.Then i get the answer ,but i want to know it can be done in harder way,i mean how to do same rotation with using complex plane .THank you in advance

corrected:how to do same rotation without using complex plane
ya that is by using trig
A stranger in comment gave this
x’= xcosa -ysina
y’= xsina +ycosa
x' and y' are new co-ordinates and x and y are old co-ordinates and a is angle
where does this formula come from

corrected:how to do same rotation without using complex plane
ya that is by using trig
A stranger in comment gave this
x’= xcosa -ysina
y’= xsina +ycosa
x' and y' are new co-ordinates and x and y are old co-ordinates and a is angle
where does this formula come from

Click to expand...

From basic trig and the application of basic trig identities.

I know you are trying very, very hard to grasp this stuff, but you mostly appear to be flailing around from topic to topic without developing the basic, foundation math knowledge and skills upon which all of this stuff is built. You can't hope to pick this stuff up piecemeal. It would be like someone trying to learn how to compose a symphony but constantly having to ask if D-flat is the same as C-sharp and not knowing that the interval between some adjacent notes is a full tone while others are a semi-tone. Your only hope is to go back and learn the foundational material. From what I have seen, that means at least going back to introductory algebra and learning it and mastering it. Then geometry. Then trigonometry. Then calculus. Along the way you need to pick up exponentials, logarithms, and complex numbers.